Multiple conductor sector electric cable



Oct. 22, 1935. N. LQ MORGAN MULTIPLE CONDUCTOR SECTOR ELECTRIC CABLE 2sheetssheet 1 Filed Nov. 13, 1951 .f/V//V/ =W r 9 a Q 2 2 n..

Oct; 22,. 1935. N L, MQRGAN 2,018,461

MULTIPLE CONDUCTO SECTOR ELECTRIC CABLE Filed NOV. 13, 1931 2SheetsSheet2 /m/f/v 70A N. L MORGAN @GMM ATTORNEY Patented Oct. 22, 1935 UNITEDSTATES PATENT OFFICE MULTIPLE CONDUCTOR SECTOR ELECTRIC CABLE YorkApplication November 13, 1931, Serial No. 574,697

2 Claims.

This invention relates to improvements in multiple conductor electriccables having sector-shaped conductors, and more particularly to themethod of making such'cables.

Sector-shaped conductors for insulated power cables may be made inseveral ways known in the art. One well known method, which is old inthe art, comprises first stranding a plurality of wires into diierentlayers, each layer being round ln shape, or substantially so, and havinga space between it and the adjacent layer, then crushing the structureto sector shape between rolls, and finallyl insulating the individualconductor after the crushing operation. In manufacturing sector-shapedconductors in accordance with this method the component wires of eachlayer are usually stranded or spiralled to forma helix; the helices orlayers of wires being stranded all in one direction throughout theconductor. 'I'he conductor, afterbelng crushed to sector shape, isusually insulated by wrapping on tapes of insulating material, such aspaper or cambric, with a suitable pitch or lay. The multiple conductors,after being insulated, are then stranded and twisted together to keepthem in proper relation to each other with the points of the' sectorspointing toward the center of the cable.

Another method known in the art consists in passing a plurality of wiresthrough a sector die, the wires, as they pass through the die, beingspirally wound around the core and laid up collectively in'sectorcross-section. Here again, the

` conductors are insulated after being formed into on the relativedirection of stranding the multiple conductors together. A tighteningaction tends to reduce the diameter of the conductor. with a consequentsoftening of the insulation and a weakening of its electricalproperties. If alternate layers of wires are stranded in oppositedirections, one layer tends to tighten and the next to loosen .andoccupy a larger space. This action often causes the conductor to departfrom its original sector shape. The same tightening and looseningactions occur in the .insulation with the result that the tapes tend tobecome wrinkled and creased and, especially in the longer lengthsl ofconductors, the insulation becomes weakened in its electricalproperties.

During the process of manufacture of the cable, it is usual, accordingto present day practice, to have the stranding together of the insulated conductors done on a diierent machine from that which insulates them.The method of the present invention may be practiced by having thestranding and insulating done on different machines. these steps areshown herein as being performed insuccession upon a single machinealthough they may be performed successively upon different machines.Both methods are within the scope of the invention.

The residual forces present in the sectorshaped conductor land itsinsulation due to the methods of manufacture outlined above frequentlyprevent the conductors from taking their proper relative position in thecable and, in some cases, a sector may become completely turned over,that is, the point of the sector conductor may point away from thecenter of the cable. This results in the cable being somewhat largerover certain sections of its length. These residual forces also tend toprevent the cable from being dead, i. e., when laid on the floor it willtend to distort or untwist itself slightly so as to be relieved of theresidual forces.

'I'hese diiiiculties are considerably reduced if not completely overcomeby manufacturing cables ln accordance with the principles underlyingthis invention.

An object of this invention is to provide an improved multi-core cablehaving sector-shaped conductors.

A feature of this invention lies in the method of insulating theindividual conductors before forming them into sector shape.

A further feature resides in the method of forcing a plurality ofinsulated conductors through a die in one operation.

One advantage of this invention is that the residual forces inherent insector-shaped cables manufactured by present day methods are greatlyreduced by constructing a cable in accordance withthis invention.

Another advantage of the present invention is that a cable is obtainedwhich has harder insulation with somewhat higher electrical -strengththan those heretofore manufactured.

A further advantage lies in the fact that the As a matter of conveniencey component wires of the conductors take up their Other objects,features and advantages will appear in the subsequent detaileddisclosure.

In accordance with this invention, the wires of the conductor are firststranded into layers which are substantially round in shape, leavingspaces between adjacent layers. The conductor is then wrapped withinsulating tape while still in the round shape. The multiple insulatedconductors are then stranded together without being twisted (that is tosay, grouping the conductors in such manner that all points on the outersurface of a conductor bear the same relative position throughout thecable with respect to other points on the same conductor). This actionprevents the tightening and loosening of the wires of the conductor andgreatly reduces the creasing and wrinkling of the insulating tapes withan accompanying reduction in the residual forces.

The stranded insulated conductors are then iormed by being forcedtogether through one or more dies; the forming forces being-transmittedto the conductor through its insulation. The circle of wires are thuscaused to collapse at the expense of the spaces between the layers. Itis to be understood that the forming forces are all y radial to thecable causing the insulated conductor to take sector shape with all thesectors pointing towards the center of the cable at all pointsthroughout its length, thus giving the cable a uniform diameter throughits entire length. During the forming operation, the perimeter of thelayers oi wires remains approximately the same but small increases inthe perimeter may cause the insulation to become tightened and stretchedto a larger perimeter thereby taking up any looseness that may havetaken place duru ing the insulating and stranding operations. Thistightening and stretching ol' the tapes (if and 'to the extent that itoccurs) makes the insulation harder and tends to give it a somewhathigher electrical strength. In practice no important tightening orloosening of the insulating tape has been observed. A cable constructedin this manu ner has no appreciable residual forces in the conductor andinsulation. For this reason, there is no noticeable tendency -of thecable to distort or untwist itself.

Referring to the drawings:

Fig. 1 represents a cross-sectional view' of a conductor prior to theapplication of the insulation thereon. This view shows the circularlayers of wires with the annular spaces between the adjacent layers;

Fig. 2 shows the conductor of Fig. l with the insulation applied. ThisView is taken along the line 2-2 of Fig. 4 which illustrates a portionof a finished conductor prior to the forming operation;-

Fig. 3 is a side perspective view of the conductor of Fig. 2. In thisview the alternate layers of wires of the conductor are shown spirallywound in opposite directions;

Figs. 4 and 5 are diagrammatic illustrations of the essentials of thestranding machines utilized in making a cable in accordance with thisinvention;

Figs. -G and 7 are side and front views respectively of the die used inchanging the round conductors to sector shape;

Fig. 8 illustrates, in cross-section, a plurality of round conductorswhich go to make up a. three- 2,il l. 8,46 1

proper relative positions causing sectors of proper conductor sectorcable, prior to the forming operation;

Fig. 9 shows the conductors of Fig. 8 after being forced through the dieof Fig. 6 and pressed to sector form.

Referring to Fig. 1, there is shown a conductor in one stage of theprocess of manufacturing a sector cable embodying the principles of thisinvention. In the conductor, a plurality of helices of wires are shownstranded in opposite directions around a single wire forming the centeror core with annular spaces between each adjacent layer of wires.Although it is desirable to have the component wires of each helixremain in a circle one or more wires in each layer might be allowed tofall in towards the center without interfering with the subsequentformation of proper sector-shaped conductors.

Surrounding the outermost layer of wires is a layer of insulation whichmay be applied directly to the conductor or by applying tapes ofinsulating material around or parallel with the conductor. These tapesmay comprise paper, varnished cambric or other material applied to theconductor with a suitable pitch or lay, applied all in one direction orby reversing different layers of tapes. When paper tapes are employed,they y are usually applied so that their edges abut while the edges ofthe cambric tapes overlap by a small amount. It is customary in the caseof paper tapes to dry them after being applied to the cable and thenhave them impregnated. With regard to the cambric tapes, however, aninsulating compound may or may not be applied between layers of tapes.The feature offirst insulating the conductors and then forming themtogether is not limited to the use of paper or fabric insulation; rubberor rubber covered fabric may also be employed.

In Fig. 4 is shown one way of constructing a 40 conductor of the typeillustrated in Figs. 1, 2 and 3 by using apparatus well known in theart.

.a roll of wire i8 mounted upon a support I9 is arranged to rotate inthe direction indicated in the drawing by the arrow, asmthe wire isdrawn 45 to the left by a capstan, not shown. This wire forms the centeror core of the conductor and is adapted to pass through mandrels ID andil upon which the successive layers of wires are helically stranded.These mandrels are hollow 50 and are held in place by supports 20 and2l. If desired, the mandrels may taper slightly at the ends 22 and 22awhere the wires of the'layers leave the mandrel. vThe layers of wiresretain their circular shape after leaving the mandrel 56 since nopressure is exerted upon them at this time.

Other rolls of wire I6, I6 and 23, 23 mounted upon gears Il carry theindividual wires which go to make up the different layers. Although 60only two rolls have been shown mounted on each gear, it is to beunderstood that there are as many rolls on each gear as there are wiresforming a layer. The gears carrying the rolls of wire are driven bypinions 24 and 25 and 65 cause the wires to be spirally wound around themandrel as they rotate, one in a clockwise direction and the other in acounterclockwise direction; the preferred lay-up being with one layerwound in one direction and the nextinthe re- 70 verse direction and soon in alternative arrangement. The rolls and mandrels are axiallyaligned, the successive mandrels increasing in size to accommodate theconductor as its size is increased by the addition of each layer.

Upon leaving the outermost mandrel, layers of insulating tape areapplied to the conductor. 'I'he tape is carried on a spool 21 mountedupon rotating gear 28 driven by pinions 29, 29. Although only one spoolof tape is shown, it is understood that there may be as many spools oftape as it is desired to have layers of insulation applied to theconductor. After the insulation is applied to the conductor, the wholeis wound while still in a round shape, on to a drinn by means of acapstan.

Fig. illustrates the manner in which three such insulated conductors aredrawn through a die to form the sector cable. Three drums 30, eachcarrying a length of conductor such as i1- lustrated in Figs. 2 and 3,are mounted on a gear 32 which is adapted to rotate upon an axis 33. Thedrums are adapted to remain in a vertical position as indicated in thedrawings as the gear rotates so that no twisting occurs as theindividual conductors are pulled through the die 34 by the capstan 35.As the conductors are spirally wound about one another, all points onthe outer surfaces of any one conductor bear the same relative positionthroughout the cable with respect to other points on the same conductor.This method of operation is well known in the art.

The round conductors are changed to sector shape as they are forcedthrough die 34 which is of suitable size; the forming forces beingtransmitted to the conductors through the insulation. 'I'hese forces,being radial to the cable, cause the circles of wires of each conductorto collapse at the expense of the spaces between the layers. Eachinsulated conductor is thus forced to take a sector shape with all thesectors in the cable pointing toward the center at all points throughoutits length, thus giving the cable a uniform diameter throughout itsentire length. It is to be noted that in the nished article thecomponent Wires of each sector conductor still retain their circularfo-rm and are not deformed by the forming operation.

In preferred practice several dies in tandem are employed to make theforming more gradual and to prevent tearing and wrinkling of theinsulating tapes. The die 3l is therefore typical of any die structureconsisting of either a. single die or a plurality of dies in tandem.Ordinarily each die will have a smaller oricethan the preceding. Theword die as employed in the claims signifies any die structureconsisting of one die or a plurality of dies in tandem. The cable may bepulled through the several dies in successive operations but to do thisin a. single operation is preferred.

In Fig. 9 is shown theY shape the individual conductors of the cable ofFig. 8 take when forced through the die during the forming operation. Inactual practice, an overall outer insulation may or may not be placedaround the cable and protected with an outer covering such as a leadsheath. The cable is then considered ready for use in the field.

In a cable constructed in accordance with the present invention thereare no appreciable residual forces either in the conductors or in theinsulation and, for this reason, there is no tendency on the part of theconductors to move from their proper positions in the cable.

What is claimed is:

l. A method of manufacturing multi-core electric cables havingsector-shaped conductors which comprises stranding the component wiresof each individual conductor into helices with spaces between layers ofadjacent helices of wire, the alternate layers of said helices beingstranded in opposite directions, wrapping insulating tapes around saidconductors while still in substantially round shape, then stranding saidconductors together and forcing them together through a die to obtainthe sector form in one operation.

2. 'I'he method of manufacturing a single conductor for a multi-coresector cable which comprises first stranding a plurality of concentriclayers of wires around a single central wire leaving spaces betweenadjacent layers, insulating

